Organic electroluminescence display device and producing method thereof

ABSTRACT

In manufacturing of an organic electroluminescence (EL) display device, after first electrodes are formed on a substrate, insulating films are formed on the first electrodes except regions corresponding to light emitting portions. Spacers are formed on the insulating films, and overhanging portions are formed so as to overhand the spacers. Thus, element isolating structure portions for isolating organic EL elements are formed. Then, organic EL films, second electrodes, and protecting films are sequentially formed between the spacers. In the tube formed light emitting portions of the organic EL display device, the bending angle of a bending portion of a pattern of the element isolating structure portion is larger than 90°.

This application is a division of prior application Ser. No. 09/653,379filed Sep. 1, 2000, which is a division of prior application Ser. No.09/274,021 filed on Mar. 22, 1999, now U.S. Pat. No. 6,147,442 which isa division of prior application Ser. No. 08/834,733 filed on Apr. 3,1997 now U.S. Pat. No. 6.037,712.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic electroluminescence displaydevice which is used as a display device or a light source and which canbe formed by a process including photolithography with easy isolation oforganic electroluminescence elements, and also relates to a producingmethod of the above organic electroluminescence display device.

2. Description of the Related Art

At present, liquid crystal display devices are used as thin flat paneldisplays which are currently the main stream of the technical field ofdisplay devices. However, organic electroluminescence (hereinafterreferred to “organic EL”) display devices using organic EL elements aresuperior to liquid crystal display devices in the following points:

(1) Having a wide viewing angle because the organic EL elements emitlight by themselves.

(2) Allowing easy manufacture of a thin display device of about 2-3 mmin thickness.

(3) Capable of providing a natural emission color because of no need forusing any polarizing plate.

(4) Capable of clear display because of a wide light and shade dynamicrange.

(5) Allowing organic EL elements to operate in a wide temperature range.

(6) Easily enabling dynamic image display because the response speed ofthe organic EL elements is three orders or more higher than that ofliquid crystal elements.

In spite of the above advantages, the organic EL display devices havethe following problems in manufacture. For example, organic layersconstituting the organic EL elements and electrodes containing a metalhaving a small work function which is usually used as a cathode toinject electrons into the organic layers are easily deteriorated bywater and oxygen. Further, the organic layers are easily dissolved by asolvent and are not resistant to heat.

In a manufacturing method using water, organic solvents, and heat, it isdifficult to isolate or divide elements after the formation of organiclayers and an electrode containing a metal having a small work function.Therefore, when it is intended to form an organic EL display device inthe same class as liquid crystal display devices currently implemented,the matured semiconductor manufacturing technology and liquid crystaldisplay device manufacturing technology cannot be applied as they are toisolate small organic EL elements.

In the above circumstance, a method has been proposed in which wallshigher than films constituting organic EL films are formed betweendisplay line electrodes to be isolated, and materials for forming theorganic EL films are vacuum-evaporated in a direction not perpendicularto the substrate surface (i.e., evaporated obliquely). This methodutilizes the fact that the materials for forming of the organic EL filmsare not formed in the portions shielded by the high walls. (Refer toU.S. Pat. Nos. 5,276,380 and 5,294,869.)

In the above method, it is very important that the directions in whichatoms or molecules travel from the evaporation source to the substratebe aligned. As shown in FIG. 8, in an ordinary evaporation method, anevaporation material is vaporized to assume concentric spheres with anevaporation source 101 in which the evaporation material is set as thecenter, and then attaches to a substrate 100. The incident angle of theevaporation material with respect to the substrate 100 varies with theposition on the substrate 100, and the thickness of a resulting filmformed on the substrate 100 varies in response to the distance from theevaporation source 101.

Therefore, it is difficult for the above method to isolate the displayline electrodes in a stable manner, and to form the films uniformly overthe entire substrate surface. Although the above method couldmanufacture small-size display devices, in order to apply the abovemethod to medium-size or large-size substrates of the 10-inch class orlarger, for example, the distance between the substrate 100 and theevaporation source 101 should be set sufficiently long. In this case,the size of the evaporation apparatus becomes impractical.

Even if such a large evaporation apparatus is produced, a large amountof organic EL material does not reach the substrate surface, and thus isconsumed in vain without being formed on the substrate, resulting in amajor factor of cost increase.

In general, a substrate is rotated or a plurality of evaporation sourcesare used to evaporate a thin film uniformly on the substrate. Thesemethods are actually employed in semiconductor device manufacturingprocesses and liquid crystal device manufacturing processes. However, ifthe above method of forming high walls is applied to these methods, theelement isolation cannot be attained any more.

In the conventional method, the organic EL films and the metalelectrodes having a small work function are necessarily exposed unlessprotecting layers are consecutively formed in the same direction. Thus,it is difficult to completely eliminate the influences of water, oxygen,etc. It is impossible to perform photolithography having a process usingan organic solvent or water after formation of the organic EL films.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a highly reliableorganic EL display device and a producing method thereof by making theelement isolation easier irrespective of the manner of evaporating anorganic EL material, enabling the use of a large-size substrate, andcompletely covering organic EL layers and metal electrodes having asmall work function by forming films that are stable with respect towater, oxygen, and organic solvents without exposing those to the air,i.e., in a vacuum.

According to the present invention, there is provided an organicelectroluminescence display device comprising: a first electrode whichis transparent and formed on a substrate; an insulating film selectivelyformed on the first electrode; a plurality of spacers formed on theinsulating film; an overhanging film which is formed on each spacer andhas a width wider than that of each spacer; an organicelectroluminescence film formed on the first electrode and betweenadjacent spacers; and a second electrode formed on the organicelectroluminescence film.

According to the present invention, there is provided a method forproducing an organic electroluminescence display device, comprising thesteps of: forming a first electrode which is transparent on a substrate;selectively forming an insulating film on the first electrode; forming aspacer film on the insulating film; selectively forming a photosensitivefilm on the spacer film; forming a plurality of spacers by overetchingthe spacer film, so that the photosensitive film overhangs each spacer;forming an organic electroluminescence film on the first electrode andbetween adjacent spacers; and forming a second electrode on the organicelectroluminescence film.

According to the present invention, there is provided an organicelectroluminescence display device comprising: a plurality of organicelectroluminescence elements; and an element isolating structure portionwhich is formed between adjacent organic electroluminescence elementsand has an overhanging portion, wherein a bending portion of the elementisolating structure portion has a bending angle larger than 90°.

According to the present invention, there is provided an organicelectroluminescence display device comprising: a plurality of organicelectroluminescence elements; and an element isolating structure portionwhich is formed between adjacent organic electroluminescence elementsand has an overhanging portion, wherein a bending portion of the elementisolating structure portion is formed by an arc having a radius ofcurvature of 5 μm.

According to the present invention, there is provided a method forproducing an organic electroluminescence display device having anelement isolating structure portion formed between adjacent organicelectroluminescence elements, a bending portion of the element isolatingstructure portion having a bending angle larger than 90°, the methodcomprising the steps of: forming a first electrode which is transparenton a substrate; selectively forming an insulating film on the firstelectrode; forming a spacer film on the insulating film; selectivelyforming a photosensitive film on the spacer film, forming a plurality ofspacers overhung by the photosensitive film by overetching the spacerfilm, to obtain the element isolating structure portion; forming anorganic electroluminescence film on the first electrode and betweenadjacent spacers; and forming a second electrode on the organicelectroluminescence film.

According to the present invention, there is provided an organicelectroluminescence display device comprising: a first electrode whichis transparent and formed on a substrate; an insulating film selectivelyformed on the first electrode; a plurality of first spacers formed onthe insulating film; a plurality of second spacers formed on the firstspacers; an overhanging film which is formed on each second spacer andhas a width wider than that of each first spacer; an organicelectroluminescence film formed on the first electrode and betweenadjacent first spacers; and a second electrode formed on the organicelectroluminescence film.

According to the present invention, there is provided a method forproducing an organic electroluminescence display device, comprising thesteps of: forming a first electrode which is transparent on a substrate;selectively forming an insulating film on the first electrode; forming aspacer film having a plurality of layers on the insulating film;selectively forming the photosensitive film on the spacer film; forminga plurality of spacers by overetching one layer of the spacer film whichis not in contact with the photosensitive film, so that thephotosensitive film overhands each spacer; forming on organicelectroluminescence film on the first electrode and between adjacentspacers; and forming a second electrode on the organicelectroluminescence film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show the structure of an organic electroluminescence(EL) elements according to a first embodiment of the invention;

FIG. 2 is a diagram explaining rotary explanation;

FIGS. 3A-3J and 4A-4C show a manufacturing process of the organic ELelement according to the first embodiment of the invention;

FIGS. 5A-5E and 7A-7B show a manufacturing process of organic ELelements according to a second embodiment of the invention;

FIG. 6 is a plan view of a color filter portion of an organic EL displaydevice according to the second embodiment of the invention;

FIG. 8 is a diagram explaining an ordinary evaporation method;

FIGS. 9A and 9B are a plan pattern view and a sectional view of lightemitting portions of an organic EL display device according to a thirdembodiment of the invention;

FIGS. 10A and 10B are a plan pattern view and a sectional view of lightemitting portions of an organic EL display device according to a fourthembodiment of the invention;

FIGS. 11A-11C are plan pattern views of a display portion of an organicEL display device according to a fifth embodiment of the invention;

FIGS. 12A-12H are plan pattern views and sectional views of a bar graphportion of the display portion of the organic EL display deviceaccording to the fifth embodiment of the invention;

FIGS. 13A-13C and 14A-14C are plan pattern views and sectional views ofa light emitting portion of an organic EL display device having elementisolating structure portions according to the invention;

FIG. 15 shows the chemical structural formula of N, N′-bis(m-methylphenyl)-N, N′-diphenyl-1, 1′-biphenyl-4, 4′-diamine;

FIG. 16 shows the chemical structural formula oftris(8-hydroxyquinoline) aluminium;

FIG. 17 shows the chemical structural formula ofpoly(tiophene-2,5-diyl);

FIG. 18 shows the chemical structural formula of rubrene;

FIG. 19 shows the chemical structural formula of 4, 4′-bis[(1,2,2-trisphenyl)ethyenyl]-biphenyl; and

FIG. 20 shows an organic EL element according to the invention with aharder film which is used as a support film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be hereinafter described indetail with reference to the accompanying drawings.

Embodiment 1

FIGS. 1A and 1B show the structure of organic electroluminescence (EL)elements according to a first embodiment of the invention. As shown inFIG. 1A, a first transparent electrode 2 (for example, an indium tinoxide (ITO) film) is formed on an insulating transparent substrate 1 ina desired pattern shape. Then, an insulating film (for example, apolyimide film or an SiO₂ film) is formed on the first transparentelectrode 2. Organic El films and second electrode contacting with theorganic EL films will be formed later to constitute a light emittingportion. A portion of the insulating film located on the display surfaceside of the light emitting portion is removed.

Next, a spacer film (for example, a polyimide film) constituted of atleast one layer is formed. After photosensitive films (photosensitiveresin films) such as resists are formed between electrodes to beisolated, photosensitive films 5 on remaining insulating films 3 areleft by photolithography. Subsequently, the exposed portions of thespacer film are removed by etching. At this time, the portions of thespacer film under the photosensitive films 5 are also removed to formsufficiently long undercut regions. As a result, with respect to thespacers 4 formed by undercutting, the photosensitive films 5 assumeseaves, hat, or cap-shaped structure, or an overhanging structure ingeneral terms. Thus, element isolating structure portions can be formed.

By forming the element isolating structure portions, when organic ELfilms 6 which control light emission and carriers and second electrodes7 directly contacting with the organic EL films 6 are formed byevaporation, as shown in FIG. 1B, the elements can always be isolatedirrespective of the positional relationship between the evaporationsource and the substrate and the method for improving the uniformity ofthe films. Thus, a method that regards, as most important, improving theuniformity of the organic EL films 6 formed, such as a rotary method inthe case of evaporation, can be selected.

After the organic EL films 6 and the second electrodes 7 directlycontacting with the organic EL films 6 are formed in the above manner,metal films 8 made of a stable metal that is hardly affected by water,oxygen, or organic solvents are formed as protecting films for thesecond electrode 7. When the organic EL films 6 and the secondelectrodes 7 are formed by evaporation, the metal films 8 are formed bya method (for example, sputtering) that provides resulting films withbetter step coverage than evaporation.

The protecting film may be any of a a metal film of a stable metal suchas aluminum (A1), an insulating film such as an SiO₂ film, and acombination of an A1 film and a second protecting film 9 such as an SiO₂film formed thereon (see FIG. 1B). The second protecting film 9 protectsthe organic EL film 6, the second electrode 7, the metal film 8, andother films.

It is desirable to form the protecting film subsequently to theformation of the organic EL film 6 and the second electrode 7 withoutbeing exposed to the air, i.e., with maintaining a vacuum state. Forexample, the protecting film may be formed by evaporation in a lowvacuum or sputtering. A film having good step coverage can be formed byrotating the substrate 1 while it is considerably inclined from thedirection of vaporization from an evaporation source 10 as shown in FIG.2.

Thus, the structure of FIG. 1B is obtained in which even the endportions of the organic EL films 6 and the second electrodes 7 are notexposed by forming the metal films 8 as the protecting films or themetal films 8 and the second protecting films formed thereon so thatthey are also formed in the above undercut regions. Since the organic ELfilms 6 are completely enclosed by the first transparent electrodes 2,the insulating films 3, and the metal films 8 (and the protecting films9), the organic EL elements can resist through a process using water oran organic solvent, such as photolithography that is performed informing lead out electrodes for the metal electrodes 8.

It is apparent from the above description that it becomes possible tocause the organic EL elements to emit light uniformly, to manufacture ahighly reliable organic EL flat panel display at a stable yield, and toincrease the flexibility of the manufacturing process of an organic ELflat panel display.

The first embodiment of the invention will be described in more detail.FIGS. 3A-3J and 4A-4C show a manufacturing process of the organic ELelements according to the first embodiment of the invention. Thisprocess is directed to a case of manufacturing a 2-row/16-column dotmatrix type display device in which the 1-dot pixel size is 0.4 mm×0.6mm and the character display area is 5×8 dots.

An inexpensive soda glass substrate, which is used in amorphous silicon(a-Si) solar cells, super twisted nematic (STN) liquid crystal displaydevices, etc., is used as the substrate of the organic El displaydevice. The entire surface of the glass substrate is coated with silica(SiO₂). The silica coating prevents sodium elution from the glasssubstrate when it is heated, protects the soda glass substrate which isnot resistant to acids and alkalis, and improves the flatness of theglass substrate surface. For example, the silica coating is performed byimmersing the glass substrate in a SiO₂ solution or by spin on glass(SOG) coating for the glass substrate.

Next, an ITO film which is transparent conductive film as a firstelectrode is formed at a thickness of about 1,500 angstrom by sputteringon the glass substrate. The use of the ITO film is due to the fact thatit exhibits superior characteristics to films made of other materialswhen it is used as a transparent conductive film. However, a transparentelectrode of a ZnO film, an SnO₂ film, or the like may be used if it hastransmittance and resistivity, for example, that will not cause anyproblem during use. When the ITO film is formed over a large area,sputtering is advantageous in uniformity and film quality of a resultingfilm as well as productivity. However, the ITO film need not always beformed by sputtering, and may be formed by evaporation, for example.

As shown in FIGS. 3A and 3F, after the ITO film is formed on thesilica-coated substrate 1 (the silica coating film is not shown), aresist pattern (not shown) is formed on the ITO film byphotolithography. After unnecessary portions of the ITO film are removedby etching to form the ITO film into a desired electrode pattern, theresist pattern is removed. As shown in FIG. 3A in enlarged form, it isdesired that the ends of the ITO films 2 be tapered. This is to prevent,in the step portions of the ITO films 2, step disconnection of organicfilms and second electrodes to be evaporated in later processes, tothereby improve the yield and life of the organic EL elements. It isdesired that the taper angle be 45° or less. Incidentally, FIGS. 3F-3Jare plan views of element patterns, and FIGS. 3A-3E are sectional viewstaken along dot-chain lines A-A′, B-B′, C-C′, D-D′, and E-E′ in FIGS.3F-3J, respectively.

Steps having a small taper angle can be formed by wet etching or dryetching. For example, in wet etching, since the etching proceedsisotropically, a taper angle of about 45° can naturally obtained if theoveretching time is not set too long. Also, in dry etching, a taperangle of 20° to 30° can easily be obtained by utilizing retreat of aresist due to the etching, that is, by selecting etching conditions suchas a dry etching gas, high frequency (e.g., RF) power and a gas pressureso that a taper angle of the resist is transferred. The etching gas forthis purpose includes gases of hydrogen halides such as hydrogenchloride and hydrogen iodide, a bromine gas, and a methanol gas.

Films for disposing spacers to be formed in a later process are formedon the ITO films 2. Any insulating film may be used as such films. Thefilms may be formed by various methods: forming inorganic thin filmssuch as SiO₂ films or SiN_(x) films by sputtering or vacuum evaporation,forming SiO₂ films by SOG coating, and applying resist, polyimide,acrylic resin or the like. Since it is necessary to expose a portion ofthe ITO films 2 formed under the insulating film, the insulating filmneeds to be patterned without damaging the ITO films 2. Although thereis no limitation on the thickness of the insulating films, when aninorganic thin film is used, the manufacturing cost can be reduced bydecreasing the thickness thereof.

It is desirable that the ends of the insulating films 3 formed above theITO film 2 be also tapered. The taper angle should be about 60° or less,preferably 45° or less. When SiO₂ films are formed as the insulatingfilms 3, a taper angle of 45° can be obtained by wet etching if theoveretching time is not set too long. To make the taper angle evensmaller, dry etching is suitable as in the case of forming the ITO films2. A carbon fluoride type etching gas such as CF₄+O₂ is generally used.

In this embodiment, polyimide is used to form the insulating films 3.Non-photosensitive polyimide to be prepared is diluted to about 5% withN-methyl pyrrolidone (NMP) or γ-butyrolactone. Such polyimide is appliedby spin coating and then prebaked at 145° C. for one hour. After apositive resist is applied, patterning is performed to form a structureshown in FIGS. 3B and 3G.

Exposed portions of the resist and corresponding portions of thepolyimide film are removed sequentially with an aqueous solution oftetra methyl ammonium hydroxide (TMAH) having a concentration of about2.38%. The TMAH is a developer for the resist. Further, only theremaining portions of the resist are removed by ethanol, to form desiredinsulating films. Although the above description is directed to the caseof using non-photosensitive polyimide, photosensitive polyimide may alsobe used. In this case, no resist is needed.

The polyimide insulating films 3 thus obtained are completely cured atabout 350° C. to prevent them from being affected by a chemicalsolution. Since the insulating films 3 contract in this process, theirsteps come to be tapered.

When the step shape of the ITO films 2 is hard to control in the abovemanner, the photomask may be so designed that the insulating films 3formed in this process also cover the step portions of the ITO films 2.

Subsequently, a spacer film to be used as spacers 4 (see FIG. 1A) isformed. Because of their purpose, the spacers 4 may be either aconductor or an insulator, and have either a single layer or amultilayer structure. However, when the spacers 4 are a conductor, thereis a possibility that metal films formed in a later process cause ashort circuit or a current leak between adjacent display lines via aspacer. This problem may be solved by making the undercut amount inetching the spacer film sufficiently large.

The spacer made of a metal has the following advantages. (1) Since thespacer is sufficiently strong and malleable, the elements that areeasily rendered faulty due to the existence of dust can sufficiently bycleaned with ultrasonic waves, for example. (2) Since the spacer is moreresistant to heat than a resist etc., dehydration can be effected byheat treatment. (3) Since the spacer is hardly charged, particles areless likely to attach to the spacer. (4) When a short circuit occurs inan element circuit due to dust, the spacer can be burnt off.

It is necessary to select an etching material for the spacer film whichneither etches nor affects the ITO films 2 that are in contact with thespacer film in etching the spacer film. Also, since the spacer film isused to form the spacer 4, it should be so formed as to be thicker thana total thickness of all of the organic EL film 6, the second electrode7, the metal film 8, the protecting film 9, and other films, as shown inFIG. 1B. Thus, it is desirable that the spacer film be made of amaterial which allows easy formation of a thick spacer film. As such amaterial film, an SOG film and a resin film are used. When the spacerfilm is made of a metal material, a laminate structure of a Cr film, aTi film, a TiN film, or other film as an etching barrier film for theITO films 2 and an Al film or other film which has a high formation ratemay be formed. The etching barrier film is not limited to a metalmaterial.

When the spacer film is made of polyimide, polyimide whose concentrationhas adjusted to 15% is spin-coated at a thickness of 2 μm, and thenprebaked at 145° C. for one hour to form a spacer film 4′ (see FIGS. 3Cand 3H). The thickness of the spacer film 4′ can be adjusted by thepolyimide concentration and the rotational speed of the spin coater.

After the formation of the spacer film 4′, a positive resist is applied.When the thickness of the positive resist is 1 μm or more, desirably 2μm or more, a highly viscous resist is used or the rotational speed ofthe spin coater is set low.

Since the positive resist is relatively fragile, the method of forming athick resist is used in this embodiment. However, as shown if FIG. 20,no such method is needed if a harder film (a second spacer) 64 is formedunder the resist 65 to support the resist 65. The use of the harder film64 as a support film has another advantage that heat treatment foreliminating water can be performed in a later process. Conversely, ifheat treatment is performed without forming the support film, the resistbecomes likely to be deformed and undercut regions may be broken. Notthat in FIG. 20, numeral 60 is a substrate, 61 is an ITO film, 62 is aninsulating film, and 63 is a spacer (a first spacer).

A conductor such as Cr, Ti, TiN, W, Mo, Ta, ITO, SnO₂ or ZnO, aninorganic insulator such as SiN_(x), SiO₂, diamond like carbon (DLC),Al₂O₃, Ta₂O₅, or glass, a semiconductor such as Si or SiC, or othermaterials can be used to form the harder film 64.

The harder film 64 can be formed by sputtering vacuum evaporation,plating, plasma chemical vapor deposition (CVD), thermal CVD or thelike. In the spacer formed by a thin film having a plurality of layers,when one layer which is in contact with a photosensitive materialconstituting the resist is not overetched, it can be used as the supportfilm for the photosensitive material. The photosensitive material can beremoved, and in this case a substrate can be baked at a heat resistanttemperature of the photosensitive material or a higher temperature.Thus, it is advantages in the case that dehydration process for asubstrate can be performed.

As described above, by applying the positive resist and then performingexposure and development to form a desired photopattern, cap-shaped (anoverhanging structure in general) photosensitive films (photosensitiveresin films) 5 are formed as shown in FIGS. 3D and 3I. The portions ofthe polyimide spacer films 4′ which are exposed when the positive resistis developed are subsequently removed by using the developer, to formspacers 4 as shown in FIGS. 3E and 3J.

The development time is determined in accordance with the undercutamount (i.e., undercut length) of the polyimide spacer film 4′. Theundercut amount is greatly influenced by the polyimide prebakingtemperature and time. In particular, the prebaking temperature needs tobe controlled so as to make the thickness of the spacer film 4′ uniformover the entire substrate surface. In this embodiment, the developmenttime is so controlled that the undercut length becomes about 4 μm. Thus,a structure shown in FIG. 3E is formed. Note that in FIG. 1A, anundercut length 39 is a length from the side surface of the spacer 4 tothe lower edge of the photosensitive film 5.

A structure shown in FIG. 4A is formed by consecutively evaporating,without exposure to the air, i.e., in a vacuum, N, N′-bis(m-methylphenyl)-N, N′-diphenyl-1, 1′-bipenyl-4, 4′-diamine (hereinafter referredto TPD; see FIG. 15) as a hole injection layer/hole transport layer ofthe organic EL film 6, tris(8-hydroxyquinoline) aluminum (hereinafterreferred to Alq₃; see FIG. 16) as a light emitting layer/electrontransport layer of the organic EL film 6, and an Mg/Ag alloy (weightratio: 10:1) film as the second electrode 7. The thickness of each ofthe TPD layer and the Alq₃ layer constituting the organic EL film 6 is500 angstrom and the thickness of the Mg/Ag alloy film constituting thesecond electrode 7 is 2,000 angstrom.

In the invention, the constituent films of the organic EL element andthe order of laying those films are not limited to those of thisembodiment. The hole injection layer, the light emitting layer, and thesecond electrode may be made of materials other than the above ones. Ahole injection layer, an electron transport layer, an electron injectionlayer, and other layers may additionally be formed to provide multilayerstructures.

In order to form the organic EL films 6, the second electrodes 7, andother layers only on the light emitting portion (i.e., display screenportion), the evaporation is performed by using a metal mask that ismounted on a substrate holder of an evaporation apparatus.

As shown in FIGS. 4A and 4B, after the formation of the organic EL films6 and the second electrodes 7, the substrate is transferred withoutexposing to the air, i.e., in a vacuum, to a vacuum chamber capable offilm formation by sputtering, so that the metal films 8 such as Al filmsare formed by sputtering. In this process, it is important that themetal films 8 be formed by a method that can provide superior stepcoverage to the method by which the organic EL films 6 having organic ELlayers are formed. In this manner, the Al films are also formed in theundercut regions, so that the organic EL films 6 which are not resistantto water and oxygen are completely shielded from the air.

The above process provides a notable advantage that the organic EL films6 can be shielded from an organic solvent used in etching, as well asfrom water and oxygen. In the conventional structure, the entire organicEL film is removed by an organic solvent that has soaked into it from anexposed portion of the film at an end portion of the pattern, forexample. Thus, once the organic EL film is formed, it is prohibited tobe in contact with any organic solvent, which restrict the kinds ofusable manufacturing processes. In contrast, the invention allows use ofa variety of manufacturing processes.

To further improve the resistance to water and an organic solvent, theprotecting films 9 such as SiO₂ films may be formed as shown in FIG. 4Bafter the metal films 8 made of a stable metal such as aluminum areformed.

In this embodiment, Al films are formed at a sputtering pressure of8×10⁻³ torr. The sputtering pressure is desired to be as high aspossible. This is because if the sputtering pressure is higher. Al atomsemitted from the Al target to various directions more likely collidewith argon atoms and are scattered, so as to go into the undercutregions more likely, whereby the organic EL films 6 are sufficientlycovered with the Al films. That is, the mean free path of Al atomsshould be shorter than the distance between the target and thesubstrate. On the other hand, if the sputtering pressure is high, theformation rate decreases due to a reduction in the voltage applied tothe target and the scattering of Al atoms. Thus, the sputtering pressureis determined by a balance between the productivity and the stepcoverage.

Although in this embodiment the metal films 8 of a stable metal such asaluminum are formed by sputtering, the invention is not limited to sucha case. For example, similar advantages are obtained by methods capableof providing good step coverage such as a method in which evaporation isperformed in a low vacuum with introduction of an inert gas, plasma CVD,and photo-assisted CVD. The same methods apply to the formation of theSiO₂ films as the protecting films 9.

By the way, when lead out Al electrode pads (not shown) are formed toconnect a control integrated circuit (IC) to the metal films 8 which arein contact with the second electrodes 7, the lead out Al electrode padsare arranged at side portions of the display portion so as not to causedefect portions on the display portion. To prevent the constituent filmsof the organic EL elements and the SiO₂ films from being formed belowand above the Al electrode pads, respectively, the Al electrode pads areshielded by the metal masks in forming the constituent films of theorganic EL elements 6 and the SiO₂ protecting films. This is to improvethe adhesiveness between the Al electrode pads and the substrate and toprevent insulating films from being formed on the Al electrode pads. Inplasma CVD and photo-assisted CVD which are much superior in coverageperformance, the SiO₂ films may be formed on the Al electrode pads evenif the metal masks are used. In such a case, connection holes reachingthe Al electrode pads may be formed by photolithography.

When insulating films such as SiO₂ films are formed as the protectingfilms 9 in the final process, even if the resist films, i.e., thephotosensitive films 5 are broken by mechanical pressure, the respectivedisplay lines would be still covered with the protecting films 9. Thus,if only the resist in the vicinity of the Al electrode pads on which noinsulating film is formed is wiped off by using a solvent, failures suchas a short circuit via constituent films of the organic EL elements willnot occur without removing the constituent films remaining on the resistin the vicinity of the display lines. The elimination of the process ofremoving the cap-shaped resist remaining over the entire substratesurface is advantageous in the manufacturing cost.

To provide more reliable organic EL elements by protecting the organicEL films from physical contact, pollution, etc., it is desirable toattach a glass substrate or the like to the organic EL elements fromabove (i.e., from the opposite side of a display surface). However, insuch a case, a solvent contained in an adhesive dissolve the resistfilms, i.e., the cap-shaped photosensitive films (photosensitive resinfilms) to possibly cause a short circuit between adjacent organic ELelements if insulating films as the protecting films are not formed inthe final process. Thus, when the glass substrate or the like forprotection is attached to the organic EL elements from above, it isdesirable to remove in advance the constituent films of the organic ELelements and Al films remaining on the photosensitive resin films. Thesefilms can easily be removed by immersing them in a chemical solutionthat can dissolve the photosensitive resin films or the spacers. Astructure shown in FIG. 4C can be formed by removing only thephotosensitive resin films by using an alcohol such as ethanol orisopropyl alcohol, an ester such as butyl acetate or ethyl acetate, oran organic solvent such as acetone or xylene.

Both the spacers 4 and the photosensitive resin films can be removed byusing a resist removing solution such as NMP, 7-butyrolactone, or typenumber MS-2001 or Fuji Hant Co., Ltd, which is on the market. In thiscase, the thin films formed on the photosensitive resin films are liftedoff. By removing also the spacers 4, the thin films on thephotosensitive resin films 5 can easily be lifted off. Thus, thisprocess is easy on manufacture.

If the spacers 4 are left as shown in FIG. 4C, they can be used asposts. That is, when the substrate for protection is attached asdescribed above, since it is not in contact with the organic EL elementsbecause of the existence of the spacers 4, physical influences of thesubstrate on the organic EL elements can be lowered and it isadvantageous on the prolongation of the life of the organic EL elements.

In this manner, the manufacturing process and the structure of theorganic EL elements may be determined in accordance with the purpose ofmanufacturing the organic EL display device, that is, depending on whichof the manufacturing cost and the life is important.

In this embodiment, only the photosensitive resin films 5 are removedand the spacers 4 are left as shown in FIG. 4C. Also, to further improvethe water resistance, carbon fluoride polymer films (not shown) areformed on the protecting films 9 by plasma CVD. Film forming gases ofCF₄ and CHF₃ to be used are decomposed at a gas pressure of 100 m torrto form the carbon fluoride polymer films. Since plasma CVD providesbetter coverage performance than sputtering, it is difficult to lift offthe photosensitive resin films 5 on the spacers 4 once the carbonfluoride polymer films are formed.

The portions of the carbon fluoride polymer films formed on the Alelectrode pads are removed by photolithography using enzyme plasma, andthen the resist is removed. Thus, a desired organic EL display device iscompleted.

In the organic EL display device thus manufactured which is superior inthe resistance to water and an organic solvent, the display lines areindependent of each other and the organic EL films are completelycovered with the stable thin films. Thus, it has been confirmed that theorganic EL display device of this embodiment is as reliable as organicEL display devices constituted of conventional organic EL elements whichoperated in a vacuum or a dried nitrogen atmosphere.

Embodiment 2

FIGS. 5A-5E and 7A-7B show a manufacturing process of an organic ELdisplay device according to a second embodiment of the invention. Thesecond embodiment is directed to the process of manufacturing a simplematrix (multiplex) type display device in which one pixel size is 330μm×110 μm, the number of pixels is 320×240×3 (RGB) dots, and colorfilters are provided. In comparison with the first embodiment, in thisembodiment, a higher resolution display device is manufactured and colorfilters are formed in advance.

FIG. 6 is a plan view of a color filter portion of the organic ELdisplay device according to the second embodiment of the invention, inwhich the top-right block and the bottom blocks are drawn in white todescribe dimensions of color filters. One pixel has a size of 330 μm×110μm. A TiN film and an Al film are shown as connecting portions C to ITOfilms which portions have a size of 30 μm×30 μm and a line L having awidth of 10 μm. FIGS. 5A-5E and 7A-7B are sectional views taken along adot line A-A′ in FIG. 6.

As the resolution increases, the electric resistance of transparentconductive films such as ITO films more likely causes a problem. Tosolve this problem, the Al films, whose resistivity is about 1/100 ofthat of the transparent conductive films, are used to form a laminatestructure with the transparent conductive films, to thereby reduce theresistance value. Since direct contact between the Al film and thetransparent conductive film causes a large contact resistance, it may bebetter to form a TiN film, a Cr film, or other film between those films.

An Al film of about 1.5 μm in thickness is formed on a transparentsubstrate (not shown) such as a glass substrate by sputtering.Immediately thereafter, a TiN film of about 300 angstrom in thickness isformed thereon by sputtering. Thus, a laminate film of the Al film andthe TiN film is formed. If the Al film and the TiN film are formed insuccession without being exposed to the air, i.e., in a vacuum, a nativeoxide film can be prevented from being formed on a surface of the Alfilm, so that good contact is obtained between the Al film and the TiNfilm. Instead of the Al film, an Al alloy film containing an elementother than aluminum may be used. To prevent uneven portions (hillocks)from being formed on the surface of the Al film due to crystal growth ofaluminum in a later heat treatment process, it is in many casesdesirable to use an Al alloy film containing scandium (Sc) or the like.

The laminate film of the Al film and the TiN film is then patterned byphotolithography to obtain Al films 11 and TiN films 12 formed thereonas shown in FIG. 5A. To obtain a high throughput and a good processedshape, the TiN film and the Al film are etched at the same time by dryetching.

The dry etching is reactive ion etching (RIE) in which the electricpower is 2,000 W, the gas pressure is 100 m torr, and etching gases areCl₂ and BCl₃. After the etching, ashing is performed without exposure tothe air, i.e., in a vacuum. This is to prevent corrosion of aluminumafter the dry etching, which is called “after-corrosion”. Wet etchingmay be performed because a poor processed shape does not cause anyserious problems.

To form color filters, a pigment dispersion type color filterapplication/formation process is performed which is most commonlyemployed as a coloring manner for liquid crystal displays. Applicationconditions for forming RGB (red, green, blue) filters at a thickness of1.0-2.5 μm are determined. In FIG. 5B, red filters 13, green filters 14,and blue filters 15 are patterned to expose the surfaces of the TiNfilms 12.

For example, the application/formation process of the red filters 13 isas follows. After a red filter solution is applied by spin coating at1,000 rpm (revolutions per minute) for about 5 seconds, prebaking isperformed at 100° C. for 3 minutes. Then, a photomask is positioned byusing an exposing apparatus, and ultraviolet light of 20 mW/cm² isirradiated for 30 seconds. Subsequently, development is performed withan about 0.1% TMAH aqueous solution. The development time is about oneminute. Further, thermal curing is performed at 200° C. for one hour sothat the red filters 13 thus formed will not be dissolved by filtersolutions of the other colors (green and blue) to be applied in thelater processes.

Because of the use of different pigments, the conditions for forming thegreen filters 14 and the blue filters 15 are somewhat different fromthose for forming the red filters 13. However, the green filters 14 andthe blue filters 15 may be formed sequentially by approximately the sameprocesses as the processes for forming the red filters 13. Thus, the redfilters 13, the green filters 14, and the blue filters 15 are formed asshown in FIG. 5B.

Although this embodiment relates to the case of forming only the colorfilters because it can be manufactured relatively easily, the inventionis not limited to such a case. For example, fluorescence conversionfilters may be used to output green light and red light through colorconversion, to provide more intense light. Further, a laminate structureof color filters and fluorescence conversion filters may be formed toprevent reduction in brightness while improving the purity of colors.

In order to improve the flatness of the forming surface of an ITO filmto be formed in a later process, an overcoat material such as polyimideor acrylic resin is applied to the red filters 13, the green filters 14,and the blue filters 15, and then patterning is performed to expose thesurfaces of the TiN films 12. Also, thermal curing is performed at about200° C. for one hour, to form overcoat layers 16 as shown in FIG. 5C.

After the formation of the overcoat layers 16, an ITO film as atransparent conductive film is formed at a thickness of about 1,400angstrom by sputtering. Further, a resist pattern is formed byphotolithography, and then the ITO film is etched with dilutehydrochloric acid. The resist is removed to form an ITO film 17 (seeFIG. 15D). Therefore, a pattern in which the transparent conductive filmand the Al film wiring that is formed to reduce the resistance areconnected to each other is formed to constitute a display line (columnline).

An SiO₂ film as an insulating film is formed on the patterned ITO film17 by sputtering, and then patterned to remain in the regions other thanthe regions where light emitting portions are seen from the side of theglass substrate (not shown), so that SiO₂ films 18 are formed (see FIG.5E). By the structure in which the ITO film 17 is covered with the SiO₂films 18, useless light emission in the regions not seen from the glasssubstrate side can be avoided. In addition, since holes or grooves arenecessarily formed in these regions, an organic EL film such as a lightemitting layer evaporated on an inclined portion may be rendered thin,to possibly form a current leak path. Thus, the formation of theinsulating film is desirable.

Although in this embodiment an SiO₂ film is used as the insulating film,the invention is not limited to such a case. Since what is needed isinsulation, not only an inorganic insulating film such as an SiO₂ filmand an SiN_(x) film but also resin such as polyimide, acrylic resin, andepoxy resin may be used. In patterning the insulating film, if a maskpattern is formed such that insulating films are left also in theregions where spacers are to be formed, a process for forming insulatingfilms under a spacer film can be omitted.

After the patterning of the SiO₂ films 18, resist films 20 having acap-shaped structure (overhanging structure in general) are formed onspacers 19 by processes similar to the processes of FIGS. 3C-3E with apolyimide film used as a spacer film (see FIG. 7A).

For a color display, light emitting elements are constructed by formingthe following materials on the structure of FIG. 7A. In this embodiment,organic EL materials are used which emit white light.

To form a yellow light emission organic EL film, polythiophene (see FIG.17) is evaporated at a thickness of 100 angstrom as a hole injectionlayer, and then TPD doped with rubrene (see FIG. 18) at 1 weight % iscoevaporated at a thickness of 500 angstrom as a hole transportlayer/yellow light emission layer. It is preferably that theconcentration of rubrene be in a range of 0.1 to 10 weight %, in thisrange high efficiency light emission is attained. The rubreneconcentration, which may be determined in accordance with the colorbalance of light emission colors, depends on the light intensity and thewavelength spectrum of a blue light emission layer to be formed in alater process. To form a blue light emission organic EL film, 4,4′-bis[(1, 2, 2-trisphenyl)ethenyl]-biphenyl (see FIG. 19) is evaporatedat a thickness of 500 angstrom as a blue light emission layer, and thenAlq₃ is evaporated at 100 angstrom as an electron transport layer. Theyare evaporated in succession without being exposed to the air, i.e., ina vacuum. Thus, organic EL films 21 are formed.

Further, an Mg/Ag alloy (weight ratio: 10:1) film is evaporated at athickness of 2,000 angstrom as second electrodes 22 without beingexposed to the air, i.e., in a vacuum. Then, Al films 23 and SiO₂protecting films 24 are formed in succession by sputtering in the samemanner as in the processes of FIGS. 4B and 4C.

Finally, the resist films 20, the various thin films formed thereon, andthe spacers 19 are removed by a removing solution, to provide a desiredsimple matrix organic EL display device as shown in FIG. 7B.

According to this embodiment, since the evaporation method can be one inwhich the uniformity of films are regarded as important, the yield canbe increased and the light emission characteristic can be made uniform.

Conventionally, a material not resistant to water or oxygen isnecessarily exposed to the air even temporarily, which decreases thereliability of organic EL elements thereby. In contrast, the inventioncan provide organic EL elements with very high reliability because theorganic EL film can be completely covered with a material that is stablewith respect to water and oxygen on each display line (pixel line).

Numerical values used in the invention are merely examples and theinvention is not limited to those values.

According to the invention, the overhanging portions wider than thespacers can easily be formed by overetching. By the existence of theoverhanging portions, the organic EL elements can be isolated easily.

According to the invention, since only the overhanging portions formedon the spacers can be removed, a sealing glass substrate or the like forsealing the entire device can easily be provided over the organic ELelements.

According to the invention, since not only the overhanging portions butalso the spacers can be removed, even an adhesive containing a solventcapable of dissolving a resist or the like can be used as the adhesivefor adhering a sealing glass substrate or the like to the device. Thisallows selection of an adhesive from a wide variety of and various kindsof adhesives.

Further, according to the invention, the protecting films constructed byat least one of an insulating film and a metal film which is stable withrespect to oxygen, water and organic solvents can be formed on thesecond electrodes by using a method that can provide better stepcoverage than methods for forming the organic films and the secondelectrodes. This allows photolithography to be conducted thereafter.Thus, the embodiment enables manufacture of an organic EL display devicehaving very high reliability and a long life.

Embodiment 3

FIGS. 13A-13C and 14A-14C are plan pattern views and sectional views ofa light emitting portion of an organic EL display device having elementisolating structure portions formed therein according to the invention.If the element isolating structure portions as shown in FIG. 1A areformed straight, the element isolation can be effected with a very highyield. However, in FIG. 13B that is a sectional view taken along a dotchain line B-B′ in FIG. 13A, the undercut length tends to be short in aregion inside a portion of an element isolating structure portion 121where it is bent at 90° or less or a region inside its curved portionhaving a small curvature. As a result, there may occur a case that thelight emitting portion and the element isolating structure portion areshort-circuited with each other via a metal film 116 made of a stablemetal that is hardly affected by water, oxygen, and organic solvents.This will cause a reduction in yield.

That is, in the case wherein light emitting portions 120 a and 120 b areisolated from each other by the element isolating structure portion 121having an overhanging structure of FIG. 13A, if the bending portionshave an angle of 90° or less, the undercut length becomes very short inthe regions inside the bending portions as indicted by a dot line in theenlarged part of FIG. 13A. As a result, when an organic EL film 114, asecond electrode 115, a metal film 116, and other films are formed ineach of the light emitting portions 120 a and 120 b, the metal film 116is formed also on the side surface of a spacer 112 in the undercutregion where the undercut length is very short as shown in FIG. 13B. Inthis manner, the metal film 116 formed above a resist 113 and the lightemitting portion 120 a and 120 b are connected to each other.

The short circuit may also occur in a region inside a curved bendingportion of the element isolating structure portion which has a radius ofcurvature of 5 μm or less.

When the element isolating structure portion 121 is formed straight asin a portion indicated by a dot chain line A-A′ in FIG. 13A, theundercut length of the spacer 112 is proper as shown in FIG. 13C that isa sectional view taken along line A-A′ in FIG. 13A. Since the metal film116 is not formed on the side surface of the spacer 112 so as to assumea thick film, the metal films 116 formed above and below the resist 113are not short-circuited with each other.

Conversely, in a region outside a bending portion (90° or less) of theelement isolating structure portion 121 (see FIG. 14A), an undercutregion 117 becomes extremely long as shown in FIG 14B that is asectional view taken along a dot chain line B-B′ in FIG. 14A. As aresult, when the overhanging body of the element isolating structureportion 121 is constituted only of a resist 113, the overhanging bodylikely hangs down as shown in FIG. 14C. This may cause a short circuitbetween the metal films 116 which are formed on the light emittingportion and the outside portion of the element isolating structureportion 121 when the metal films 116 are formed.

To reduce the number of lead out electrodes of a display device havingcomplicated patterns, it is necessary to form element isolatingstructure portions that meander. It is desired to increase the yield informing those element isolating structure portions.

When a bending portion of the element isolating structure portion has anangle of 90° or less or it is curved at a small radius of curvature of 5μm or less, the reason why the undercut length varies with the shape ofthe plan pattern is considered non-uniformity in the degree of theaction that an etching chemical goes around to act on the spacer film.Thus, in a region where the undercut length tends to be short, it isexpected that the non-uniformity can be avoided by employing a planpattern that allows an etching chemical to go around more easily.

It has been confirmed that a marked increase in yield can be obtained byforming a photomask pattern that is free of a portion where the elementisolating structure portion is bent at a small angle of 90° or less as asimplest but effective method for attaining a plan pattern that allowsan etching chemical to go around more easily in undercutting the spacerfilm.

Although a pattern bending angle larger than 90° is effective, thebending angle should be 100° or more and, more desirably, 135° or more.In experiments, portions having a bending angle of 135° show adifference in undercut length of only 30% as compared to straightportions. That is, it has been confirmed that the undercut lengthdecreases by 30% in regions inside such bending portions from that ofthe straight portions, and that it increases by 30% in regions outsidethe bending portions.

When an organic EL display device having the element isolating structureportions on a substrate is manufactured by using the above describedpattern, no short circuit is observed in the bending portions. A similarincrease in yield is obtained by forming circular arc patterns havingradii of curvature that are larger than 5 μm.

The third embodiment of the invention will be described in a morespecific manner with reference to FIGS. 9A and 9B, which are planpattern views and sectional views of light emitting portions of anorganic EL display device according to the third embodiment of theinvention. In FIG. 9A, an element isolating structure portion 31isolates light emitting portions 32 a and 32 b constituted of organic ELfilms and other films. The element isolating structure portion 31 iscomposed of a resist 33 and a spacer 34, and regions inside its bendingportions are bent at an angle of 135°.

In FIG. 9B that is a sectional view taken along a dot chain line A-A′ inFIG. 9A, the regions inside and outside the spacer 34 which are formedunder the resist 33 have sufficiently long undercut lengths of about 3μm and about 4 μm, respectively. Thus, no short circuit occurs when ametal wiring film is formed on this structure.

As described above, according to the invention, a flat panel displayusing organic EL elements which can be manufactured at a stable, highyield and enables various lighting patterns is obtained.

Embodiment 4

FIGS. 10A and 10B are plan pattern views and sectional views of lightemitting portions of an organic EL display device according to thefourth embodiment of the invention. In FIG. 10A, an element isolatingstructure portion 31′ isolates light emitting portions 32 a′ and 32 b′constituted of organic EL films and other films. The element isolatingstructure portion 31′ is composed of a resist 33′ and a spacer 34′, andregions inside its bending portions assume circular arcs having a radiusof 10 μm.

In FIG. 10B that is a sectional view taken along a dot chain line A-A′in FIG. 10A, the regions inside and outside the spacer 34′ formed underthe resist 33′ have sufficiently long undercut lengths of about 3 μm andabout 4 μm, respectively. Thus, no short circuit occurs when a metalwiring film is formed on this structure.

Embodiment 5

FIGS. 11A-11C are plan pattern views of a display portion of an organicEL display device according to a fifth embodiment of the invention, andFIGS. 12A-12H are plan pattern views and sectional views of a bar graphportion of the display portion of the above organic EL display device.The fifth embodiment is directed to a case of manufacturing a 2-digitdigital counter with a bar graph.

FIG. 11A is a view of a 2-digit digital counter as viewed from theorganic EL film side (i.e., the bask side) rather than from thetransparent substrate side (i.e., the display side), and is hence amirror image of an ordinary view as viewed from the display side. FIG.11A also shows light emitting regions as viewed from the organic EL filmside.

FIG. 11B shows a relationship between the pattern of ITO films(indicated by dot lines) formed on a substrate 40 and openings (wherethe ITO films are exposed; indicated by solid lines) that are obtainedby partially removing an insulating film formed on the ITO films.

FIG. 11C shows element isolating structure portions 41 a and 41 b, anarea E where organic EL films and second electrode portions are formed,and an area S where metal wirings made of a stable metal hardly affectedby water, oxygen, and organic solvents and protecting films are formed.The element isolating structure portion 41 a isolates the bar graph fromthe numeral displaying portion as well as isolates the bar graph intotwo sections. The element isolating structure portion 41 b encloses thenumeral display portion.

After the openings (indicated by solid lines) are formed by partiallyremoving the insulating film formed on the pattern of the ITO films(indicated by dot lines) as shown in FIG. 11B, the element isolatingstructure portions 41 a and 41 b are formed as shown in FIG. 11C. Asdescribed later, the element isolating structure portions 41 a and 41 bare formed with a pattern in which every bending portion has a bendingangle of 135°. The element isolating structure portion 41 a includes aslant straight portion 41 a′ formed at the center of the 2-figure bargraph.

After the element isolating structure portions 41 a and 41 b are formed,organic EL films and second electrodes containing a metal having a smallwork function are formed by evaporation in the area E indicated by thedot chain line, and metal films and protection films are formed in thearea S indicated by the two-dot chain line (see FIG. 11C). At this time,a common electrode C1 is connected to the metal film of the elementisolating structure portion 41 a-1 located on the right side of theslant straight portion 41 a′, and a common electrode C2 is connected tothe metal electrode of the element isolating structure portion 41 a-2located on the left side of the slant straight portions 41 a′. A commonelectrode C3 is connected to the metal electrode of the elementisolating structure portion 41 b.

A manufacturing process of the bar graph will be described withreference to FIGS. 12A-12H. FIGS. 12A-12D are plan views of the bargraph pattern, and FIGS. 12E-12H are sectional views taken along dotchain lines A-A′, B-B′, C-C′, and D-D′ in FIGS. 12A-12D, respectively.

An inexpensive soda glass substrate is used as a substrate 40 for anorganic EL display device. A silica coating is performed for the entiresurface of the substrate 40. The silica coating prevents sodium frombeing eluted from the glass substrate when it is heated, protects thesoda glass substrate that is not resistant to acids and alkalis, andimproves the flatness of the glass substrate surface.

Next, an ITO film which is a transparent conductive film as a firstelectrode is formed at a thickness of 1,000 angstrom on the glasssubstrate 40 by sputtering. The use of the ITO film is due to the factthat it exhibits superior characteristics to films made of othermaterials when used as a transparent conductive film. However, atransparent electrode of a ZnO film, SnO₂ film, or the like may also beused if it has transmittance and resistivity, for example, that will notcause any problem during use. When the ITO film is formed over a largearea, sputtering is advantageous in uniformity and film quality of aresulting film as well as productivity. The ITO film need not always beformed by sputtering, and may be formed by evaporation, for example.

After a resist pattern is formed on the formed ITO film byphotolithography, unnecessary portions of the ITO film are removed byetching and then the resist is removed, to leave a desired electrodepattern of the ITO film 41 (see FIGS. 12A and 12E).

Next, a film for determining the light emitting regions is formed on theITO film 41. Any insulating film may be used as this film. The film maybe formed by various methods: forming an inorganic thin film such as anSiO₂ film or an SiN_(x) film by sputtering or vacuum evaporation,forming an SiO₂ film by SOG coating, and applying resist, polyimide,acrylic resin, or the like. Since it is necessary to expose a portion ofthe ITO films 41 formed under the insulating film, the insulating filmneeds to be patterned without damaging the ITO film 41. Although thereis no limitation on the thickness of the insulating film, when aninorganic thin film is used, the manufacturing cost can be reduced bydecreasing the thickness thereof.

In this embodiment, polyimide is used to form the insulating film.Non-photosensitive polyimide to be prepared is diluted to about 5% withNMP or γ-butyrolactone. Such polyimide is applied by spin coating, andthen prebaked at 145° C. for one hour. After a positive resist isapplied, patterning is performed (see FIGS. 12B and 12F).

Exposed portions of the resist and corresponding portions of thepolyimide film are removed sequentially with an aqueous solution of TMAHhaving a concentration of about 2.38%. TMAH is a developer for theresist. Further, only the remaining portions of the resist are removedby ethanol, to form a desired insulating film 42. Although the abovedescription is directed to the case of using non-photosensitivepolyimide, photosensitive polyimide may also be used. In this case, noresist is needed.

The polyimide insulating film 42 thus obtained is completely cured at atemperature not higher than 350° C. so as not to be affected by chemicalsolutions to be used in later process. Since the insulating film 42contract at this time, the steps are tapered. Thus, a pattern forexposing only the light emitting portions and connecting portions toexternal circuits is obtained (see FIG. 12B)

Subsequently, a spacer film to be used as a spacer 43 is formed (seeFIG. 12G). Because of their purpose, the spacer 43 may be either aconductor or an insulator, and have either a single layer or multilayerstructure. However, when the spacer 43 is a conductor, there is apossibility that metal films formed in a later process cause a shortcircuit or a current leak between adjacent display lines via a spacer43. This problem may be solved by making the undercut amount in etchingthe spacer film sufficiently large.

As described above, the spacer made of a metal has the followingadvantages. (1) Since the spacer is sufficiently strong and malleable,the elements that are easily rendered faulty due to the existence ofdust can sufficiently be cleaned with ultrasonic waves, for example. (2)Since the spacer is more resistant to heat than a resist etc.,dehydration can be effected by heat treatment. (3) Since the spacer ishardly charged, particles are less likely to attach to the spacer. (4)When a short circuit occurs in an element circuit due to dust, thespacer can be burnt off.

It is necessary to select an etching material for the spacer film whichneither etches nor affects the ITO film 41 that are in contact with thespacer film in etching the spacer film. Also, since the spacer film isused to form the spacer 43, it should be so formed as to be thicker thanall of an organic EL film, a second electrode, a protecting film, andother films. Thus, it is desirable that the spacer film be made of amaterial which allows easy formation of a thick spacer film. Examples ofsuch a film are an SOG film and a resin film. When the spacer film ismade of a metal material, a laminate structure of a Cr film, a Ti film,a TiN film, or other film as an etching barrier film formed on the ITOfilm 41 to prevent their etching and an Al film or other film which hasa high formation rate may be formed. The etching barrier film is notlimited to a metal material.

When polyimide is used to form the spacer 43, polyimide whoseconcentration has been adjusted to 15% is spin-coated at a thickness of2 μm, and then prebaked at 145° C. for one hour. The thickness ofpolyimide can be adjusted by the concentration of the solution to beapplied by spin coating and the rotational speed of the spin coater. Thepolyimide film can be made thicker by increasing the concentration ordecreasing the rotational speed.

Subsequently, a positive resist is applied to the prebaked polyimidefilm. When the thickness of the positive resist is not less than 1 μm,desirably not less than 2 μm, a highly viscous resist is used or therotational speed of the spin coater is set low.

Since the positive resist is relatively fragile, the method of forming athick resist is employed in this embodiment. However, no such method isneeded if a harder film is formed and then a resist is applied thereon,i.e., if a harder film is formed under the resist to support the resist,as described above. That is, it is not necessary to increase a thicknessof the resist. The use of the harder film such as a support film hasanother advantage that a dehydration treatment by heating foreliminating water absorbed on the substrate surface can be performed ina later process. Conversely, if a heat treatment is performed withoutformation of the support film, the resist becomes likely to be deformedand undercut regions may be broken. Further, if the support film is madeeven stronger, since the overhanging portions remain even after removalof the resist, dehydration by heating the substrate to a temperature nolower than the maximum heat resistant temperature of the resist can beperformed. Thus, as described above, the structure as shown in FIG. 20can be also formed so that the harder film 64 as the support filmsupports the resist 65 as a photosensitive material.

Exposure and development are performed to form a desiredphotolithography pattern of the element isolating structure portion 41a. Portions of the polyimide film which are exposed by this resistdevelopment are also removed subsequently to the removal of the resist.

As shown in FIG. 12C, even in bending portions of the pattern which maybe given an angle of 90°, the number of bending portions is increased toprovide larger bending angle. That is, the patterning is so made thatthe bending portions have a bending angle of 135°.

The undercut amount of the polyimide film formed under the resist isdetermined based on the development time. The undercut amount is alsogreatly influenced by the polyimide prebaking temperature and time. Inparticular, it is necessary to control the prebaking temperature so thatthe film quality of the polyimide film be uniform over the entiresubstrate surface. In this embodiment, the development time is sodetermined that the undercut length becomes about 4 μm. In this manner,as shown in FIG. 12G, an element isolating structure portion having thepolyimide spacer 43 and a resist 44 is formed similar to that of FIG.1A.

Next, TPD as a hole injection layer/hole transport layer of an organicEL film, Alq₃ as a light emitting layer/electron transport layer of theorganic EL film, and an Mg/Ag alloy (weight ratio: 10:1) film as asecond electrode are consecutively evaporated in a consecutiveevaporation chambers without being exposed to the air, i.e., in avacuum. The thickness of each of the TPD layer and the Alq₃ layer is setat 500 angstrom and the thickness of the Mg/Ag alloy layer is set at2,000 angstrom.

In the invention, the constituent films of the organic EL element andthe order of laying those films are not limited to those of thisembodiment. The hole injection layer, the light emitting layer, and thesecond electrode may be made of materials other than the above ones. Ahole injection layer, an electron transport layer, an electron injectionlayer, and other layers may additionally be formed to provide laminatestructures. Further, the thicknesses of the respective films are notlimited to those of the embodiment. That is, the invention is applicableirrespective of the kinds of film forming materials and the structure ofthe films.

The respective films of TPD, Alq₃, and the second electrode are formedonly in the area E by using a metal mask provided in the evaporationapparatus. In FIGS. 12D and 12H, an organic EL constituent film 45including the organic light emitting layer includes organic films suchas TPD and Alq₃ and the second electrode.

After the evaporation of TPD serving as the hole injection layer/holetransport layer, Alq₃ serving as the light emitting layer/electrontransport layer, and the second electrode, a TiN film and an Al film areformed in succession by sputtering without being exposed to the air,i.e., in a vacuum, to form a metal wiring film 46 (see FIG. 12H). TheTiN film is formed between the Al film and the patterned ITO film as theconnection electrode terminal to improve the contact performance betweenthose films.

The metal wiring film 46 is formed via the metal mask. The opening sizeof the metal mask is so designed that the metal wiring film is notformed on the portions where lead out wirings for the ITO film locatedoutside the area enclosed by the two dot chain line (see FIG. 11C) areconnected to external circuits. Thus, the metal wiring film 46 is formedonly in the area S enclosed by the two dot chain line in FIG. 11C.

The resulting digital counter with the bar graph is divided by theelement isolating structure portions 41 a-1, 41 a-2, and 42 a. The threesecond electrodes are provided therein (see FIG. 11C). The commonelectrode C3 for numeral display is always grounded electrically. Thecommon electrodes C1 and C2 are supplied with a voltage having anoperation frequency of 60 Hz and a duty ratio of ½; that is, they aresupplied with the grounding voltage and the same voltage as the firstelectrode alternately.

When the common electrode is not divided, the number of electrodeterminals connected to the bar graph portion is the same as the numberof electrode terminals connected to the numeral display portion, i.e.,10. In this case, the common electrode is shared by the bar graphportion and the numeral display portion. On the other hand, if thecommon electrode is divided, the number of total terminals can be made7: 5 terminals that are connected to the first electrodes plus 2terminals for the common electrodes C1 and C2. As such, the invention iseffective in dividing common electrodes of various shapes with a highyield.

Although this embodiment is directed to the case where the bendingportions of the plan pattern of the element isolating structure portionshave an angle larger than 90°, the same advantages can be obtained evenin a case where the bending portions of the plan pattern are so formedas to assume circular arcs having a radius of curvature larger than 5μm.

As described above, by etching the spacer film so that the undercutlength does not have a large variation (the uniformity of the undercutlength is improved) in the regions inside and outside the bendingportions of the plan pattern of the element isolating structureportions, overhanging portions are overhang by a sufficient amount inthe above inside and outside regions. Thus, organic EL elements can beisolated certainly.

The invention provides the following superior advantages:

(1) Since the bending portions of the plan pattern of the elementisolating structure portions having an overhanging structure have angleslarger than 90°, the yield of element isolation can be increasedremarkably. If the angles of the bending portions are made 135° or more,the element isolating structure portions can be formed while a shortcircuit is completely avoided in the bending portions.

(2) Since the bending portions of the plan pattern of the elementisolating structure portions are formed by circular arcs having radii ofcurvature larger than 5 μm, the yield of element isolation can beincreased remarkably. If the radii of curvature of the circular arcs ofthe bending portions are 10 μm or more, the element isolating structureportions can be formed while a short circuit is completely avoided inthe bending portions.

(3) Since the uniformity of the undercuts of the element isolatingstructure portions are greatly improved, an organic EL display devicecan be manufactured at a high yield. Further, since the secondelectrodes of various shapes which are isolated electrically can beformed, an organic EL display device of the invention can be applied toproducts of various kinds of display method.

What is claimed is:
 1. An organic electroluminescence display panelcomprising; a plurality of organic electroluminescence devices, each ofthe organic electroluminescence devices comprising: a substrate; a firstconductive electrode provided on the substrate, the first electrodedefining a step area proximate a first edge thereof; an insulating layerprovided on the substrate over at least a portion of the first electrodeso that the insulating layer is located over the step area; an organicelectroluminescent layer disposed on the substrate; and a secondconductive electrode provided on the substrate in a location such thatthe organic electroluminescent layer is disposed between the first andsecond conductive electrodes thereby forming the organicelectroluminescence device; and wherein isolation between theneighboring organic electroluminescence devices is accomplished by anisolating structure portion having an overhanging portion on theinsulating layer between regions where the neighboring organicelectroluminescence devices are formed, and organic electroluminescentlayers and second conductive electrodes are formed on the insulatinglayer and the isolating structure portion.
 2. An organicelectroluminescence display panel in accordance with claim 1, where abending portion of the isolating structure portion has a bending angleof larger than 90 degrees.
 3. An organic electroluminescence displaypanel in accordance with claim 1, wherein a bending portion of theisolating structure portion is formed by an arc having a radius ofcurvature of 0.5 micron meter or more.
 4. An organic electroluminescencedisplay panel in accordance with claim 3, wherein the isolatingstructure portion further comprises a spacer which is formed under theoverhanging portion and includes a metal.
 5. An organicelectroluminescence display panel in accordance with claim 1, whereinthe insulating layer includes a photo-sensitive acrylic material or aphoto-sensitive oly-imide material.
 6. An organic electroluminescencedisplay panel in accordance with claim 1, wherein the insulating layerincludes an upper surface that defines an angle of 60 degrees or lesswith an upper surface of the first conductive electrode proximate thestep area.
 7. An organic electroluminescence display panel in accordancewith claim 6, wherein the angle is 45 degrees or less.
 8. An organicelectroluminescence display panel in accordance with claim 6, whereinthe upper surface of the first conductive electrode is substantiallyflat and is substantially horizontally aligned.
 9. An organicelectroluminescence display panel in accordance with claim 1, whereinthe first conductive electrode is substantially transparent to visiblewavelengths of light, and the substrate is substantially transparent tovisible wavelengths of light.
 10. An organic electroluminescence displaypanel in accordance with claim 1, which further comprises a second steparea along another edge of the first conductive electrode and whereinthe insulating layer also covers the second step area, and wherein theinsulating layer is photo-imaged so as to define a via or aperturetherein over a central area of the first conductive electrode so thatthe organic electroluminescent layer can contact the first conductiveelectrode through or via the aperture defined in the insulating layer.11. An organic electroluminescence display panel comprising: a pluralityof organic electroluminescence devices, each of the organicelectroluminescence devices comprising; a substrate; at least oneconductor formed on the substrate; a first insulator layer formed on theat least one conductor and the substrate, wherein the insulator layerincludes at least one pixel opening formed therein defining a pixelarea, wherein the first insulator layer includes a uniformly slopingsurface surrounding the pixel area; a second insulator layer formed onthe first insulator layer; and an organic electroluminescent layerformed on the at least one conductor in the pixel area wherein theorganic electroluminescent layer extends over the uniformly slopingsurface of the first insulating layer; and wherein isolation between theneighboring organic electroluminescence devices is accomplished by anisolating structure portion having an overhanging portion on theinsulating layer between regions where the neighboring organicelectroluminescence devices are formed, and organic electroluminescentlayers and second conductive electrodes are formed on the insulatinglayer and the isolating structure portion.
 12. An organicelectroluminescence display panel in accordance with claim 11, wherein abending portion of the isolating structure portion has a bending angleof larger than 90 degrees.
 13. An organic electroluminescence displaypanel in accordance with claim 11, wherein a bending portion of theisolating structure portion is formed by an arc having a radius ofcurvature of 0.5 micron meter or more.
 14. An organicelectroluminescence display panel in accordance with claim 13, whereinthe isolating structure portion further comprises a spacer which isformed under the overhanging portion and includes a metal.
 15. Anorganic electroluminescence display panel in accordance with claim 11which further comprises a sealing assembly secured to the substrate forenclosing the first insulator layer, the second insulator layer, theorganic electroluminescent layer and a portion of the at least oneconductor.